A diffraction grating having a periodic structure is used as a spectroscopic element in various apparatuses. In particular, a structure formed of metal having high X-ray absorptance is used in nondestructive inspection of an object and in the medical field.
One example of applications of the structure formed of metal having high X-ray absorptance is a shield grating (absorption grating) of an image pickup apparatus that performs imaging using Talbot interference of X-rays. An imaging method using the X-ray Talbot interference (X-ray Talbot interferometry) is one of imaging methods that use X-ray phase contrast (X-ray phase imaging).
A brief description of the X-ray Talbot interferometry will be given. In general image pickup apparatuses that perform the X-ray Talbot interferometry, spatially coherent X-rays pass an object and an X-ray diffraction grating to form an interference pattern. A shield grating that periodically blocks X-rays is placed at a position where the interference pattern is formed to form moire. The moire is detected by a detector, and an image is acquired using the detection result.
Common shield gratings used in Talbot interferometry have a structure in which X-ray transmitting portions and X-ray shield portions are periodically arranged. Many X-ray shield portions have a structure formed of metal having high X-ray absorptance, such as gold, and having a high aspect ratio (the ratio of the height or depth h of the structure to its width w (h/w)). A known method for manufacturing a shield grating whose shield portions have such a structure fills a mold with metal by soldering.
PTL 1 discloses, as a method for manufacturing a shield grating, a method of forming recessed sections in a silicon substrate by reactive ion etching and depositing metal in the recessed sections by soldering.